Smoke and heat detector incorporating an improved smoke chamber

ABSTRACT

A novel smoke and heat detector incorporating an improved smoke chamber. The smoke detector includes a radiation detector mounted orthogonally to a radiation source emitting a beam of non-visible radiation through the smoke chamber. The radiation detector measures the radiation scattered by smoke particles in the chamber, initiating an alarm whenever a dangerous level of smoke is detected. A self-test circuit is provided for electronically simulating a predetermined concentration of smoke to test the radiation detector circuitry and the alarm. The alarm is also enabled by a fault detection network if the radiation source becomes non-operative. The smoke chamber includes a novel deflector apparatus for channeling air through the chamber in a substantially vertical direction and through the point where the optimum detection angle of the radiation detector intersects the incident radiation beam. Moreover, a high-temperature, low-heat source is positioned near the top of the chamber to establish a large temperature differential between the ambient input air and air leaving the chamber, maximizing air flow through the chamber.

United States Patent [191 [111 3,882,477 Mueller May 6, 1975 [5 SMOKEAND HEAT DETECTOR INCORPORATING AN IMPROVED SMOKE 57 ABSTRACT CHAMBER[76] Inventor: Peter H. Mueller, 517 S. Gunderson,

Oak Park, Ill. 60304 22 Filed: Mar. 26, 1973 211 App]. No.: 344,532

US. Cl. 340/237 S; 340/411; 356/207 Int. Cl. G08b 17/12 Field of Search340/237 S, 228 S; 250/373,

[56] References Cited Primary Examiner-John W. Caldwell AssistantExaminer-Daniel Myer Attorney, Agent, or Firm-Merriam, Marshall, Shapiro& Klose A novel smoke and heat detector incorporating an improved smokechamber The smoke detector includes a radiation detector mountedorthogonally to a radiation source emitting a beam of non-visibleradiation through the smoke chamber. The radiation detector measures theradiation scattered by smoke particles in the chamber, initiating analarm whenever a dangerous level of smoke is detected. A self-testcircuit is provided for electronically simulating a predeterminedconcentration of smoke to test the radiation detector circuitry and thealarm. The alarm is also enabled by a fault detection network if theradiation source becomes non-operative. The smoke chamber includes anovel deflector apparatus for channeling air through the chamber in asubstantially vertical direction and through the point where the optimumdetection angle of the radiation detector intersects the incidentradiation beam. Moreover, a high-temperature, low-heat source ispositioned near the top of the chamber to establish a large temperaturedifferential between the ambient input air and air leaving the chamber,maximizing air flow through the chamber.

17 Claims, 7 Drawing Figures INFRARED SIGNAL RADIATION RADIATION mom/01vA85 some: FAULT I5, I I parser/01v I l SCATTERH) :vsrwomr I jfRAD/ATIONt y DUETO J L a SMOKE 24 I20 VOLTAGE SIGNAL fl'fg/Zfigf, REFERENCE p cmSIGNAL SIGNAL 22 slow. s z IO caMmRAmR slow as 25 LOCK-UP nsser SIGNALNETWORK 30 SWITCH S se -gh 5 ,5 rslaml. 26

ALARM PATENTED HAY 975 SHEET 1 FIG./

INFRARED SIGNAL RADIATION RADIATION I RADIATION l SOURCE ,6 ABSORBERFAULT 34 I8 I I DETECTION I I SCATTERED NETWORK RADIATION V Y DUE TO L.SMOKE 24 I20 INFRARED VOLTAGE SIGNAL REFERENcE 5%??273:

SIGNAL SIGNAL .32 SIGNAL 32 I0 b COMPARATOR ag SIGNAL SIGNAL fi vifik 30RESET SWITCH SIGNAL HEAT sENsoR SIGNAL I I ;26

ALARM Pas. v

LED

PATENTEDNM 61.975 882,477

SHEET 3 Hill;

J "it I.

SMOKE AND HEAT DETECTOR INCORPORATING AN IMPROVED SMOKE CHAMBER Thisinvention relates to smoke and heat detector apparatus and in particularto such apparatus where smoke warning or alarm is provided afterdetecting dangerous levels of smoke particles.

Reference may be made to the following US. Pat. Nos.: 3,504,184;3,505,529; 3,534,351 3,430,220;

3,555,532; 3,579,216; 3,585,621; and 3,659,278.

A variety of smoke detecting devices have been used for many years inwhich visible light emitting means are situated so as to direct visiblelight through a smoke chamber. If there are smoke particles present inthe chamber the radiation is scattered by the smoke particles anddetected by a photocell for initiating an alarm.

Such smoke detection systems using visible radiation have encounteredseveral problems in use. In particular, the incandescent filament lampsgenerally used as the source of visable light, radiate heat which oftencauses problems with various heat sensitive compo nents in the system.Moreover, incandescent lamps are themselves prone to failure as a resultof heat build-up with in the lamp or due to mechanical shock such asthat resulting from careless handling of the device. In addition, as theincandescent lamps ages, its efficiency and therefore its outputradiation level drops off so that the sensitivity of the system isalways changing and finally becomes too low for reliable operation.Another often annoying problem is due to the attractiveness of thevisible light from incandescent lamps to various bugs which collect inthe smoke chamber, scatter the light and set off numerous false alarms.Many of the above problems can be partially solved with increasedmaintenance, however, this is economically prohibitive in systemsinvolving hundreds of such detectors. Even in single unit usage, such asin homes, the improbability of the required maintinance being performedoften makes these units impractical.

It has therefore been suggested to use light emitting diodes (LEDs)instead of incandescent lamps in smoke detector systems. It is currentlypossible using available semiconductor light emitting diodes to obtain along lasting, reliable unit with minimum maintinance. However, it is noteasy to determine whether the radiation source is operating properlywhen such detectors are normally mounted in locations which are notreadily accessible. Standard fail-safe techniques used for incandescentfilament type lamps require several additional components, areexpensive, and do not lend any assistance in solving this problem sinceonly an open circuit lamp condition needs detection. With the LED, thediode may be opened or shorted, and in either case some indication mustbe given to prevent erroneous and possibly dangerous reliance on aninoperative smoke detector unit. Moreover, prior art self-testarrangments have been limited to testing the power supply and the alarmwithout checking the critical detection circuits.

Prior art smoke detectors have commonly included a smoke chamber forcontinuously channeling room air past a smoke detection arrangement todetect dangerous concentrations of smoke within the room. To improve airflow through the chamber, several prior art systems have utilized heatsources, such as incandescent lamps or power resistors, to warm the airso that a convection draft is created. However, as heat is radiatedthroughout the chamber, the air at the input is warmed, and thetemperature differential between air entering the chamber and airleaving the chamber decreases. This, in turn, actually reduces air flowthrough the chamber. Moreover, the room air may be heated by a fire,reducing air flow through the chamber, before a sufficient level ofsmoke is developed to trigger an alarm. In fact, it is possible that thefirst alarm may be initiated only after the heat sensor is enabled.

SUMMARY OF THE INVENTION In accordance with the principles of thepresent invention, there is provided a smoke particle detector utilizinga radiation emitting semiconductor device as a radiation source totransmit a non-visible radiation beam and a radiation detector toreceive scattered radiation and trigger an alarm when dangerous levelsof smoke particles are present. The radiation source and detector havematching spectral radition characteristics so as to greatly increase thedetection efficiency. The complementary detection circuit furtherenables overall system efficincy to be maintained fairly constant with aminimum of maintenance required. Following detection of scatteredradiation, a comparator circuit is triggered to lock up an alarm therebyindicating the presence of dangerous smoke levels.

Relatively inexpensive fault detection apparatus also is included todetect either an open circuit or a short circuit condition of thesemiconductor light emitting diode and to indicate an alarm. The faultdetection apparatus operates directly into the system comparator circuitand alarm lock-up apparatus and does not require an additional powersources for operation.

Self-test apparatus is further included to provide a self-contained testcapability for electronically simulating the effect of dangerous levelsof smoke. The entire smoke detection portion of the apparatus can bechecked, resulting in alarm activation if the components are in properoperating condition.

The smoke particle detector also includes a novel smoke chamber having ahigh-temperature low-heat source for maximizing air flow through thesmoke chamber over a wide range of temperatures by maintaining a largetemperature differential between incoming and outgoing air. The smokechamber is further effective to channel the air flow through the chamberat the point where the incident radiation beam is optimumly scattered tothe radiation detector.

The resulting smoke detector constructed in accor dance with the presentinvention thus utilizes desirable infrared radiation and a novel smokechamber for smoke particle detection, and includes inexpensivecomponents in providing required fail-safe and selftesting features.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a schematic blockdiagram of smoke and heat detector constructed in accordance with theprinciples of the present invention;

FIG. 2 illustrates a schematic circuit diagram of the electroniccomponents in a smoke and heatdetector according to FIG. 1;

FIG. 3 illustrates an alternative embodiment of a failsafe feature;

FIG. 4 is a perspective view of a novel smoke chamber used inconjunction with the smoke and heat detector shown in FIGS. 1 and 2;

tures thereof; and

FIG. 7 is a sectional view of the smoke chamber taken along lines 77 inFIG. 6.

DETAILED DESCRIPTION Referring now to FIGS. 1 and 2, there isillustrated a smoke and heat detector I in which non-visiable infraredradiation is scattered by smoke particles, de tected and amplified toenergize an alarm. The smoke and heat detector 10 includes an infraredradiation source 12 emitting non-visible radiation directly towardsinfrared radiation absorber 14 at one end of the smoke chamber 16. Ifthere are smoke particles present in the chamber 16, the non-visibleradiation is deflected and scattered by such smoke particles as shown bythe dashed lines 18 to infrared radiation detector 20 which is mountedtransversely to the direct non-visible infrared beam.

Infrared detector 20 provides a detected signal to a comparator 22 whichcompares the signal level from detector 20 with the incoming signallevel from a voltage reference 24. The comparator 22 is set at athreshold level related to voltage reference 24 so that the detectorwill be sensitive to smoke caused by burning materials common to homesand offices, but will not be accutely sensitive to usual levels ofcigarette, cigar or pipe smoke. Thus the system will only be activatedby dangerous levels of smoke to provide a signal through lock-up network25 to the alarm 26. A reset switch 28 is provided for overriding thelock-up network 25 and shutting off the alarm 26 as desired. In additionto smoke detection, the device includes an indepenedent heat sensor 30for detecting dangerous levels of heat above 135 F. so as to actuate thealarm 26..

A fail-safe feature is included through fault detection network 34 forindicating a non-operating radiation source 12 without requiringadditional expensive power sources and components. Provision is alsoincluded in the detector 10 for initiating a self-test of severalcomponents in the detector. As is shown in FIG. 1, a test switch 32 whenoperated places a signal into infrared radiation detector 20 of anamplitude just sufficient to inititate alarm 26. This self-testingprocedure thus checks the radiation detector, comparator, lockupnetwork, alarm and AC power source.

Referring now to FIG. 2, there is illustrated a schematic circuitdiagram of a preferred embodiment of the smoke and heat detector 10. Theinfrared radiation source 12 comprises a radiation emitting device suchas a light emitting semiconductor device emitting short infraredradiation 18 at detector 20 is due to scattering from smoke particles inchamber 16. Thus, in the presence of smoke particles, some of the directinfrared radiation is scattered and detected by infrared detector 20mounted in the smoke chamber at right angles to the IR-LED 12. Thedetector 20 comprises a photoconductive field effect transistor (FET)having gate, drain and source electrodes labeled G, D, and S asindicated on FIG. 2.

Comparator transistor 40 includes an emitter element coupled toreference point 42 at one end of Zener diode 44. The other end of Zenerdiode 44 is connected back to back with a silicon diode 46 in atemperature compensated arrangement. Zener diode 44 and diode 46 may bereplaced by a tapped temperature compensated diode or a bipolartransistor wherein the baseemitter junctions serves as a Zener diode andthe basecollector junction serves as a silicon diode. Reference point 42is maintained at about 6.2 volts by a 10 volt Zener diode 48 maintainingjunction point 50 at [0 volts supplied from the rectified AC powersource 52. Dropping resistior 54 drops the voltage from 10 volts atjunction point 50 to the reference point 50 to the referecne 6.2 voltsat reference point 42.

Resistors 58 and 60 comprise a voltage divider network across the 6.2volt reference to properly bias the photodector FET 20. Thephotodetector FET 20 typically needs from I to 4 volts bias and this isprovided by coupling its gate element G through resistor 56 to thevoltage divider. Resistor 99 is coupled between the source element S andsaid reference point 42 to provide source degeneration thereby improvingthe linearity of the photodetector FET 20. Further, the draincurwavelength infrared radiation (IR-LED) in the smoke light emittingdiodes producing radiation at wavelengths other than in the infraredregion may also be used.

The radiaiton absorber l4 absorbs substantially all of the directradiation from the lR-LED 12, so that any rent is adjusted to provide anessentially zero temperature coefficient. If there is no scatteredinfrared radiation impressed on photodector FET 20, the drain element Dis at about 13 volts.

Alternatively, the photoconductive FET 20 can be replaced by a bipolartransitor if the biasing arrangement is appropriately revised. Ofcourse, the selftemperature compensation feature of the photoconductiveFET 20 would not then be available.

The drain element D is coupled to the base of a common emitter DCamplifier 62, DC coupled with source degeneration through Zener diode64. The source degeneration decreases the gain of amplifier 62 andlinearizes it at the same time. The pupose of the 5.6 volt Zener diode64 is to give a voltage level shift such that the DC amplifier can be DCrealistically. In addition Zener diode 64 is a positive temperaturecoefficient device of approximately 0.035% perC. Bipolar transistor 62exhibits a negative temperature coefficient at the base-emitter junctionof approximately the same value. Thus diode 64 and the bipolar PNPtransistor 62 provide a DC amplifier with very linear gaincharacteristics 7 and almost a zero temperature coefficient. Zener diode64 and bipolar transistor 62 may be thermally bonded to each other if ahigh degree of compensation is desired over large temperature ranges.

The collector of the transistor 62 is connected to a series combinationof two resistors66 and 68 such that when there is no smoke in thechamber 16 there is approximately a four volt drop across these tworesistors at point 70. Connection point 70 is also tied to the base ofcomparator transistor 40. When smoke is present in the chamber and someof the energy from the infrared light emitting diode 12 is scattered inthe direction of the FET 20 the voltage at point 70 is changed fromabout 4 volts towards 6.7 volts, which is enough to trigger ontransistor 40. The comparator transistor 40 is turned on, thus alsoturning on transistor 72 and drawing operating current through a relaysolenoid coil 74. Normally open relay contacts 76 then close to operatebuzzer alarm 78. Other alarm, warning or indicating devices may insteadbe operated as desired.

It may be noted that once smoke is detected and the alarm 78 energized,continued smoke need not be pres ent in the chamber to keep the alarmenergized. A

locking circuit is provided by diode 80 which conducts and connects apositive voltage to point 70 at the input to the comparator transitor40, forcing this transistor to remain on. The collector electrode oftransistor 40 is coupled to the anode of diode 80 through the collectorcircuit of transitor 72 thereby providing a positive feedback path. Ifthere is no longer any smoke in the chamber, the system can be reset bydepressing momentary reset switch 82 to short out the input to thecomparator and thereby turn off the alarm. However, alarm turn off willonly be momentary if there is still smoke present in chamber 16, sinceupon release of the reset switch the comparator transitor 40 will againbe triggered to energize the alarm.

An automatic resetting heat sensor 84 is also provided to operate atapproximately 135 F. and directly connect buzzer alarm 78 to anoperating voltage. Thus, whenever the temperature of the surroundingatmosphere is greater than 135 R, an alarm will be given, regardless ofthe smoke detector components. The alarm 78 will automatically be shutoff when the ambient temperature drops below about 130 F.

A distinct feature of the present invention is the initiation of afail-safe procedure in the event that the light emitting diode 12 is nolonger operating. In the event of a failure of the diode 12, a faultdetection network 34 operates to activate the comparator transistor 40so as to turn on the alarm. It must be realized of course that the useof an extremely reliable light emitting diode 12 as opposed to the usualincandescent, visible light emitting devices of the prior art makes itextremely remote that the infrared radiation source (i.e., LED 12) wouldfail. However, the radition source is such a very important component ofthe system that it is extremely desirable to provide an alarm shouldthis component fail. As opposed to prior art techniques utilizingseparate expensive power sources and extra components for the fail-safeprocedure, the present invention instead utilizes diodes 90 and 92 as afault detection network between the infrared light emitting diode 12 andthe comparator 22.

Referring now to FIG. 2, it can be seen that the diode 90 has its anodeelement connected to one end of the infrared light emitting diode 12 atreference point 94. The cathode end of diode 90 is connected toreference point 70 at the input to the base element of comparatortransistor 40. Assuming that the infrared light emitting diode 12 hasbecome open circuited. reference point 94 will rise to about 9 volts.This forward biases diode 90 and being coupled into reference point 70drives comparator transistor 40 on. When transistor 40 is triggered,transistor 72 is triggered, and the alarm is given in the same manner asif smoke had been detected in the smoke chamber 16.

If the infrared light emitting diode 12 becomes shorted, diode 92,having its cathode connected to reference point 94 and its anodeconnected to reference point 95 intermediate silicon diode 46 and Zenerdiode 44, is forward biased to drive the photo F ET 20 and activate thealarm circuit as if smoke had been detected. This operation is providedas follows. Under normal circumstances, about 6.2 volts are present atreference point 42. In addition, silicon diode 46 is normally forwardbiased so that there is about 0.6 volt at reference point 95 whichresults from the normal forward bias voltage drop for silicon diodes. Onthe other hand, diode 92 is a germanium diode which normally exhibits amuch lower forward bias voltage drop of about 0.2-0.3 volts as comparedto the silicon diode 46. Thus, if we assume that the infrared lightemitting diode 12 is shorted, this forward biases germanium diode 92 anddrops the votage at reference point 95 from about 0.6 volts to about 0.3volts. This reduces the voltage at point 42 from the normal 6.2 volts toabout 5.9 volts, which represents about a 5% change in voltage atreference point 42. Since the gate bias voltage for the photo FET 20 issupplied through resistors 56, 58, 60, this same percentage of voltagechange is reflected back to the gate bias voltage to turn on the photoFET 20. Transistor 62 then turns on raising the voltage at referencepoint to trigger on the comparator transistor 40 and turn on the alarmthrough transistor 72 as in normal smoke detection.

In either case, if the light emitting diode 12 is not operating becauseof being opened or shorted, comparator transistor 40 is constantlyturned on so that the alarm will always be activated. Thus, even if theoperator momentarily depressed reset switch 82 to momentarily short outthe input of transistor 40 and cut off the alarm, the alarm would goback on again when the momentary push button switch 82 was released. Theconstant activation of alarm 78 reminds the user and thus encourages himto disconnect the smoke detector from the main power line so that itwill not be relied upon to preform its normal functions until theinfrared diode 12 is replaced and the units can thereafter be put backinto service.

The aforementioned fail-safe technique is particularly useful for homeinstallations of the smoke detector 10. The normal home user is nottechnically oriented and therefor a continuous sounding buzzer or otheralarm safely discourages him from attempting to rely on a defectivesmoke detector unit, i.e., one in which the IR-LED fails to operate.

In large, commercial or industrial plants incorporating a large quanityof smoke detectors 10 in a smoke warning system, it would be annoyingand unnecessary to continuously sound an audio alarm upon failure of theIR-LED in one unit. Industrial and commerical smoke warning systemsnormally provide a degree of overlapping between individual detectorunits as a cer tain measure of fail-safe protection. In such systems itis only necessary to indicate visually at a central alarm office thefailure of an IR-LED in a particular unit. Thus, diodes and 92 may beremoved, and the voltage developed at junction 94 can be coupled to amain control panel where any deviation from the standard voltage is tobe interpreted as a radiation source failure. Accordingly, the alarm 26may consist of a light operating or not operating at the central office.Alternatively, such visual indication may be provided on each individualunit, as shown for instance in FIG. 3. A visible LED 96 normally drawingabout 20 milliampers is placed in parallel across a LED 97 which isnormally drawing about 250-300 milliamperes. If LED 97 becomes an' opencircuit and fails to operate, the visible low power LED 96 is requiredto draw in excess of I milliamperes and soon burns out. In the event LED97 shorts out, the voltage across the visible LED 96 is reduced to sucha level that it cannot be put into conduction. Thus, in either event avisual indication is given denoting a failure in the LED 97.

Testing of all of the remaining components of the smoke detector isaccomplished by momentarily depres sing test switch 98 which shorts outthe source resistor 99 in series with the FET source element. Thischanges the bias level supplied to the FET 20 and fur ther drops thevoltage level at the drain element, D. If the comparator and alarmcomponents of the smoke detector are operating normally, the transistor62 is turned on so as to trigger comparator transistor 40 and transistor72 so as to activate the alarm 78. Failure of the alarm 78 to activateindicates there is some component failure in the detector, comparator,lock on network or alarm sections of the smoke detector. If an ACcoupled system is utilized, this test feature may be incorporatedtherein. However, instead of shorting resistor 99, a small portion ofthe sinusoidal or pulsed signal from the radiation source 12 must becoupled to the source element S of photo FET 20 via a switch. Again, thephoto FET 20 interprets this signal as indicative of a dangerousconcentration of smoke, and the alarm 78 is enabled.

Referring now to FIGS. 4 and 5, there is shown a novel smoke chamber,identified generally at 100, which is useful for optimumly channeling acontinuous air sample through the smoke and heat detector previouslydescribed. The smoke detector 100 comprises an open-ended main chamber102 having a cross slotted tube 104 traversing one wall of the chamberfor mounting a radiation source 12 (e.g., a light emitting diode)therein. Consequently, a beam of incident radiation (I) is transmittedacross the main chamber 102.

A radiation detector is mounted in a tube 106 traversing the back Wallof the chamber, orthogonally to the incident radiation beam (I) emittedby the radiation source 12. Consequently, an alarm is sounded whenever apredetermined level of radiation is deflected from the incident beam anddetected by the radiation detector 20.

A radiation absorber 14 is mounted opposite the radiation source 12 andexternal to the chamber 102 for absorbing any of the incident radiation(I) that is not deflected by the smoke particles so that it will not bereflected to the detector 20, triggering a false alarm. Further, all theinterior surfaces of the smoke chamber 100 have a flat black finish toprevent reflection of the incident radiation beam from the chamber wallsto the radiation detector 20. In addition, the detector 20 is set backin tube 106 to reduce the reflected radiation which it sees. Thus, theradiation detector 20 will dete ct only that radiation scattered withinits radiation detection envelope where it intersects the incidentradiation beam (I). Accordingly, to effect maximum sensitivity, the airflow should be channeled to the point where the incident radiation beam(I) and the optimum detection angle of detector 20 intersect.

As may be more clearly seen in FIGS. 6 and 7, a bottom cover 108 and abottom deflector plate 110 positioned at the bottom of main chamber 102combine to direct a continuous flow of air to the back of the chamber.An oppositely disposed top deflector 112 affixed tothe back wall ofchamber 102 near its top end forces the air toward the front of thechamber so'that it is substantially channeled through the center of themain chamber 102. Having passed out the top end of chamber 102, the airis directed out of the smoke chamber by an output deflector 114 and thetop cover 116. As shown in FIG. 7, the top deflector 112 and the outputdeflector 114 may be combined into an integrated deflection unit.

The bottom cover 108 and the top cover 116 combine with the bottomdeflector 110, the top deflector 112, and the output deflector 114 toprevent external radiation from entering the smoke chamber 100 therebyminimizing any possibility that the calibration of a smoke detectionsystem will be affected.

To insure that the air flow is centered at the intersection of theincident radiation beam (I) and the optimum detection angle of detector20 with respect to the side walls of the chamber 102 as well as thefront and back walls, the top deflector 112 and the top cover 1 16 havenotches 112a and 116a, respectively, centered on their edges tofacilitate air flow in a substantially vertical direction through thecenter of the main chamber 102. It should be noted that the direction ofair flow is substantially vertical which is the optimum direction of airflow since there is minimum drag effect on the chamber walls and thereis less resistance due to gravity.

To maximize air flow through the main chamber 102, a high-temperaturesource, such as the hightemperature resistor 118 shown in the presentembodiment, is positioned in the space between the top deflector 112 andthe top cover 116 to maintain a substantial temperature differentialbetween air exiting the smoke chamber 100 from the top cover 116 and theambient air entering through 'the bottom cover 108. More particularly,in the present embodiment, a pair of ceramic insulator sleeves 120located in opposite side walls of the top cover 116 facilitateconnection of the hightemperature resistor 114 to the external smokedetector circuitry (FIG. 2) while properly positioning the resistor 118to maximize air flow.

In order to maximize the air flow, it is important to maintain asubstantial temperature differential between incoming ambient air andair leaving the smoke chamber over a wide range of ambient airtemperatures. That is, the volume of a gas, such as air, is directlyproportional to the absolute temperature of the gas irregardless of heattransfer. As the air near the output of the smoke chamber 100 (i.e.,high temperature resistor l 18) expands, the weight per unit volumedecreases because there are fewer molecules found therein. Accordingly,the gravitational pull on the air decreases proportionately, causing theless dense air to rise and be replaced by the cooler ambient air fromthe input. Thus, a continuous air sample is effectively drawn throughthe smoke chamber 100. If, on the other hand, the air at the input is atvery nearly the same temperature, the air entering the smoke chamber 100is for all practical purposes as dense as the air leaving the chamber sothat the amount of air flowing through the chamber is decreased.

Because the high-temperature resistor 118 is capable of continuousreliable operation at temperatures above 600 F. while dissipating only asmall amount of power,

typically less than 3 watts, it is especially well-suited to maintain alarge temperature differential between the input and output of the smokechamber 100 over a wide range of ambient air temperatures. Typical powerresistors, however, which are primarily designed to dissipate heat donot operate at high temperatures. On the other hand, any heattransferred from the high temperature resistor 118 to the surroundingair in smoke chamber 100 is rapidly removed from the upper por tion ofthe chamber by the updraft of air.

Accordingly, the smoke chamber of the present invention is effective tomaintain a large temperature differential (e.g., in the order of 500 F.)between incoming ambient air and air leaving the chamber even when theambient air approaches temperatures at which prior art systems usingheat transfer to create convection currents would be ineffective.

As an alternative embodiment, the radiation absorber may be replaced bya substantially parabolic reflector which is highly reflective at wavelengths corresponding to the incident radiation beam (I) frequency. Byproperly focusing the reflective beam to be incident at the intersectionof the incident beam and the optimum detection angle of radiationdetector 20, the radiation source 12 can be operated at a reduced powerlevel while retaining the same system sensitivity. Or, the radiationsource power may be maintained to further increase the detectorsensitivity since more photons are then passed through the scatteringregion. Another parabolic reflector having an aperture to pass theincident radiation beam (1) may be positioned at the radiation source 12for subsequently reflecting the reflected radiation. It may also bedesirable to position a third reflector on the chamber wall oppositeradiation detector 20 to focus radiation scattered away from theradiation detector 20 back towards the radiation detector therebyincreasing the sensitivity of the smoke detector system.

Thus, it can be seen that there has been provided a very reliable smokedetector unit utilizing an infrared light emitting diode and a novelsmoke chamber with significant advantages obtainable over prior artvisible light smoke detectors. In addition, there is also providedeconomical means for achieving a fail-safe feature and providingself-testing with this desirable infrared smoke detecting technique.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom as modifications will be obvious to those skilled in the art.

I claim:

1. A smoke detector for detecting the presence of smoke particles withina smoke chamber, said smoke detector comprising:

radiation source means including a radiation emitting semiconductordevice for transmitting a beam of radiation within said smoke chamber;

radiation detector means for receiving radiation scat tered from saidbeam by said smoke particles, said radiation detector means providing adetected sig nal representative of the concentration of said smokeparticles in said smoke chamber;

alarm means for generating a warning signal whenever said detectedsignal indicates that a dangerous concentration of said smoke particlesis present within said smoke chamber; and

self-test means for electronically simulating a preselectedconcentration of said smoke particles just sufficient to cause saidradiation detector means to enable said alarm means.

2. A smoke detector for detecting the presence of smoke particles withina smoke chamber, said smoke detector comprising:

radiation source means including a radiation emitting semiconductordevice for transmitting a beam of radiation within said smoke chamber;

radiation detector means for receiving radiation scattered from saidbeam by said smoke particles, said radiation detector means providing adetected signal representative of the concentration of said smokeparticles in said smoke chamber;

alarm means for generating a warning signal whenever said detectedsignal indicates that a dangerous concentration of said smoke particlesis present within said smoke chamber; fault detection means for enablingsaid alarm means responsive to said radiation source being disabled as aresult of said light emitting semiconductor device being short-circuitedor open circuited; and

self-test means for electronically simulating a preselectedconcentration of said smoke particles just sufficient to cause saidradiation detector means to enable said alarm means.

3. A smoke detector for detecting the presence of smoke particles withina smoke chamber, said smoke detector comprising:

radiation source means including a radiation emitting device fortransmitting a beam of radiation within said smoke chamber; radiationdetector means for receiving radiation scattered from said beam by saidsmoke particles, said radiation detector means providing a detectedoutput signal representative of the concentration of said smokeparticles in said smoke chamber;

voltage reference means developing a substantially constant referencevoltage;

comparator means for generating a control signal whenever said detectedoutput signal exceeds said threshold level,

said comparator means including a transistor having base, emitter andcollector electrodes, said reference voltage being coupled to saidemitter electrode for establishing a conduction threshold level for saidcomparator transistor corresponding to a dangerous concentration of saidsmoke particles, said detected output signal being coupled from saidradiation detection means to said base electrode, said comparatortransistor being turned on to generate a control signal at saidcollector electrode when said base electrode is biased to exceed saidconduction threshold responsive to a dangerous concentration of saidsmoke particles; and

alarm means coupled to said collector electrode for generating a warningsignal whenever said comparator means generates said control signal.

4. A smoke detector in accordance with claim 3 wherein said radiationdetector means includes a photo-conductive field effect transistor (FET)having an output electrode coupled to said comparator base electrode,said voltage reference means being coupled to said FET for biasing saidFET to develop a detected output signal voltage at said output electrodeproportional to the amount of radiation scattered by said smokeparticles and impinging on said FET, said FET detected output signalvoltage biasing said comparator base electrode to turn on saidcomparator transistor if said conduction threshold of said comparatortransistor is exceeded.

5. A smoke detector in accordance with claim 4 including fault detectionmeans comprising first and second electronic switch means for enablingsaid alarm means responsive to said radiation emitting device beingshort-circuited or open-circuited, said first electronic switch meansbeing coupled between said radiation source means and said voltagereference means to reduce said reference voltage for simultaneouslyreducing said comparator conduction threshold below the level at whichsaid comparator base electrode is biased and increasing the bias appliedto said-PET to increase said detected FET output voltage to bias saidcomparator transistor to conduction responsive to said radiationemitting semiconductor device being short-circuited, said secondelectronic switch means being coupled between said radiation sourcemeans and said comparator base electrode to bias said comparatortransistor to conduction responsive to said light emitting semiconductordevice being open-circuited, said comparator transistor being turned onresponsive to either condition to enable said alarm means despite theabsence of a dangerous concentration of said smoke particles.

6. A smoke detector in accordance with claim 5 wherein said voltagereference means includes a Zener diode and a semiconductor deviceserially coupled between said conductor emitter electrode and two planesof differing reference potential for establishing said constant voltagethreshold level, said FET being coupled to the junction of said Zenerdiode and said semiconductor device for said bias, said first electronicswitch means comprising a diode coupled between said radiation emittingdevice and the junction of said Zener diode and said semiconductordevice, said diode being conductive to reduce said reference voltageapplied to said comparator emitter electrode and lower said conductionthreshold thereof and to bias said FET to turnon said comparatortransistor if said radiation emitting device is short-circuited.

7. A smoke detector in accordance with claim 5 wherein said secondswitch means comprises a diode coupled between said radiation emittingdevice and said comparator base electrode.

8. A smoke detector in accordance with claim 4 including test switchmeans for increasing the bias applied to said FET to electronicallysimulate a preselected concentration of said smoke particles and causesaid FET to develop said detected output voltage signal just sufficientto exceed said comparator threshold level and enable said alarm means,said test switch means being effective to check said radiation detectormeans, said comparator and said alarm means for 7 12. proper operation.9. A smoke detector in accordance with claim 3 including fault detectionmeans comprising a visible lightemitting semiconductor device coupled inparallel with said radiation emitting device, said visible lightemitting semiconductor device producing a visual light as long as saidradiation emitting device is operative.

10. A smoke detector in accordance with claim 3 including switch meanscoupled to said comparator collector electrode for enabling said alarmmeans responsive to said comparator transistor being turned on.

11. A smoke detector in accordance with claim 10 including lock-up meansfor biasing said comparator base electrode to maintain said comparatortransistor in a conductive state thereby enabling said alarm means eventhough the detected signal applied to said baseelectrode hassubsequently dropped below said conduction threshold.

12. A smoke detector in'accordance with claim 11 including a resetswitch for overriding said lock-up means and disabling said alarm meansafter said detected signal has dropped below said conduction threshold.

13. A smoke detector in accordance with claim 11 wherein said lock-upmeans comprises a semiconductor switching device coupled between saidcomparator collector electrode and said base electrode, saidsemiconductor switching device being conductive to apply a portion ofthe output voltage developed at said collector electrode to said baseelectrode when said comparator transistor is turned on.

14. A smoke detector in accordance with claim 13 wherein saidsemiconductor switching device comprises a diode.

15. A smoke detector in accordance with claim 3 wherein said radiationdetector means includes a photoconductive semiconductor devicepositioned substantially orthogonal to said radiation emitting devicefor detecting said scattered radiation and developing output signalrepresentative of the concentration of said smoke particles.

16. A smoke detector in accordance with claim 3 including radiationabsorber means positioned on the opposite side of said smoke chamber forabsorbing said radiation beam to prevent said beam from being reflectedto said radiation detector means, said radiation absorber means insuringthat any of said radiation detected by said radiation detector means isa result of scattering said beam by said smoke particles.

17. A smoke detector in accordance with claim 3 including heat sensormeans for detecting dangerous levels of heat and enabling said alarmmeans, said heat sensor means being independent of said radiation sourcemeans and said radiation detector means.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3, 882,477

DATED May 6, 1975 lNV ENTOR(S) Peter H. Mueller It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 24, change "with in" to within--; Column 2, line 9,change "the to --a;

line 33, change "an" to -any-;

line 57, after "of" insert -a-; Column 4, line 27, change "photodector"to -photodetector-; Column 6, line 67, change "milliampers" tomilliamperes-; Claim 6, line 31, change "conductor" to -comparator-.

Signed and Sealed this thirtieth Day of September 1975 [SEAL] .1

Arrest:

RUETH C. MA SON I C. MARSHALL DANN Allvslmg Ofjim Commisxioner ofPurenls and Trademarks

1. A smoke detector for detecting the presence of smoke particles withina smoke chamber, said smoke detector comprising: radiation source meansincluding a radiation emitting semiconductor device for transmitting abeam of radiation within said smoke chamber; radiation detector meansfor receiving radiation scattered from said beam by said smokeparticles, said radiation detector means providing a detected signalrepresentative of the concentration of said smoke particles in saidsmoke chamber; alarm means for generating a warning signal whenever saiddetected signal indicates that a dangerous concentration of said smokeparticles is present within said smoke chamber; and self-test means forelectronically simulating a preselected concentration of said smokeparticles just sufficient to cause said radiation detector means toenable said alarm means.
 2. A smoke detector for detecting the presenceof smoke particles within a smoke chamber, said smoke detectorcomprising: radiation source means including a radiation emittingsemiconductor device for transmitting a beam of radiation within saidsmoke chamber; radiation detector means for receiving radiationscattered from said beam by said smoke particles, said radiationdetector means providing a detected signal representative of theconcentration of said smoke particles in said smoke chamber; alarm meansfor generating a warning signal whenever said detected signal indicatesthat a dangerous concentration of said smoke particles is present withinsaid smoke chamber; fault detection means for enabling said alarm meansresponsive to said radiation source being disabled as a result of saidlight emitting semiconductor device being short-circuited or opencircuited; and self-test means for electronically simulating apre-selected concentration of said smoke particles just sufficient tocause said radiation detector means to enable said alarm means.
 3. Asmoke detector for detecting the presence of smoke particles within asmoke chamber, said smoke detector comprising: radiation source meansincluding a radiation emitting device for transmitting a beam ofradiation within said smoke chamber; radiation detector means forreceiving radiation scattered from said beam by said smoke particles,said radiation detector means providing a detected output signalrepresentative of the concentration of said smoke particles in saidsmoke chamber; voltage reference means developing a substantiallyconstant reference voltage; comparator means for generating a controlsignal whenever said detected output signal exceeds said thresholdlevel, said comparator means including a transistor having base, emitterand collector electrodes, said reference voltage being coupled to saidemitter electrode for establishing a conduction threshold level for saidcomparator transistor corresponding to a dangerous concentration of saidsmoke particles, said detected output signal being coupled from saidradiation detection means to said base electrode, said comparatortransistor being turned on to generate a control signal at saidcollector electrode when said base electrode is biased to exceed saidconduction threshold responsive to a dangerous concentration of saidsmoke particles; and alarm means coupled to said collector electrode forgenerating a warning signal whenever said comparator means generatessaid control signal.
 4. A smoke detector in accordance with claim 3wherein said radiation detector means includes a photo-conductive fieldeffect transistor (FET) having an output electrode coupled to saidcomparator base electrode, said voltage reference means being coupled tosaid FET for biasing said FET to develop a detected output signalvoltage at said output electrode proportional to the amouNt of radiationscattered by said smoke particles and impinging on said FET, said FETdetected output signal voltage biasing said comparator base electrode toturn on said comparator transistor if said conduction threshold of saidcomparator transistor is exceeded.
 5. A smoke detector in accordancewith claim 4 including fault detection means comprising first and secondelectronic switch means for enabling said alarm means responsive to saidradiation emitting device being short-circuited or open-circuited, saidfirst electronic switch means being coupled between said radiationsource means and said voltage reference means to reduce said referencevoltage for simultaneously reducing said comparator conduction thresholdbelow the level at which said comparator base electrode is biased andincreasing the bias applied to said FET to increase said detected FEToutput voltage to bias said comparator transistor to conductionresponsive to said radiation emitting semiconductor device beingshort-circuited, said second electronic switch means being coupledbetween said radiation source means and said comparator base electrodeto bias said comparator transistor to conduction responsive to saidlight emitting semiconductor device being open-circuited, saidcomparator transistor being turned on responsive to either condition toenable said alarm means despite the absence of a dangerous concentrationof said smoke particles.
 6. A smoke detector in accordance with claim 5wherein said voltage reference means includes a Zener diode and asemiconductor device serially coupled between said conductor emitterelectrode and two planes of differing reference potential forestablishing said constant voltage threshold level, said FET beingcoupled to the junction of said Zener diode and said semiconductordevice for said bias, said first electronic switch means comprising adiode coupled between said radiation emitting device and the junction ofsaid Zener diode and said semiconductor device, said diode beingconductive to reduce said reference voltage applied to said comparatoremitter electrode and lower said conduction threshold thereof and tobias said FET to turn-on said comparator transistor if said radiationemitting device is short-circuited.
 7. A smoke detector in accordancewith claim 5 wherein said second switch means comprises a diode coupledbetween said radiation emitting device and said comparator baseelectrode.
 8. A smoke detector in accordance with claim 4 including testswitch means for increasing the bias applied to said FET toelectronically simulate a preselected concentration of said smokeparticles and cause said FET to develop said detected output voltagesignal just sufficient to exceed said comparator threshold level andenable said alarm means, said test switch means being effective to checksaid radiation detector means, said comparator and said alarm means forproper operation.
 9. A smoke detector in accordance with claim 3including fault detection means comprising a visible light emittingsemiconductor device coupled in parallel with said radiation emittingdevice, said visible light emitting semiconductor device producing avisual light as long as said radiation emitting device is operative. 10.A smoke detector in accordance with claim 3 including switch meanscoupled to said comparator collector electrode for enabling said alarmmeans responsive to said comparator transistor being turned on.
 11. Asmoke detector in accordance with claim 10 including lock-up means forbiasing said comparator base electrode to maintain said comparatortransistor in a conductive state thereby enabling said alarm means eventhough the detected signal applied to said base electrode hassubsequently dropped below said conduction threshold.
 12. A smokedetector in accordance with claim 11 including a reset switch foroverriding said lock-up means and disabling said alarm means after saiddetected signal has dropped below said conductIon threshold.
 13. A smokedetector in accordance with claim 11 wherein said lock-up meanscomprises a semiconductor switching device coupled between saidcomparator collector electrode and said base electrode, saidsemiconductor switching device being conductive to apply a portion ofthe output voltage developed at said collector electrode to said baseelectrode when said comparator transistor is turned on.
 14. A smokedetector in accordance with claim 13 wherein said semiconductorswitching device comprises a diode.
 15. A smoke detector in accordancewith claim 3 wherein said radiation detector means includes aphotoconductive semiconductor device positioned substantially orthogonalto said radiation emitting device for detecting said scattered radiationand developing output signal representative of the concentration of saidsmoke particles.
 16. A smoke detector in accordance with claim 3including radiation absorber means positioned on the opposite side ofsaid smoke chamber for absorbing said radiation beam to prevent saidbeam from being reflected to said radiation detector means, saidradiation absorber means insuring that any of said radiation detected bysaid radiation detector means is a result of scattering said beam bysaid smoke particles.
 17. A smoke detector in accordance with claim 3including heat sensor means for detecting dangerous levels of heat andenabling said alarm means, said heat sensor means being independent ofsaid radiation source means and said radiation detector means.